This project utilizes single neuron recording and operant conditioning techniques on behaving monkeys to study brain mechanisms underlying voluntary movement. Monkeys are trained to make movements of a handle whose position controls a visual display, and stimuli are delivered via the handle by means of an electronically controlled torque motor in order to determine how sensory feedback is processed. A major focus of work in this project has been neural activity in putamen, which is an input stage for a group of interconnected subcortical neuronal aggregates collectively referred to as the basal ganglia. Putamen receives inputs from the cerebral cortex and thalamus, is reciprocally connected with the substantia nigra pars compacta, and projects to the globus pallidus, a basal ganglia output stage. Microelectrode recordings in monkeys have shown that some putamen neurons have tonic spontaneous discharge in absence of movement; the more numerous putamen neurons that are phasically related to voluntary movement do not exhibit tonic activity in absence of movement. The tonic putamen neurons may be the cholinergic interneurons that are intrinsic to the putamen, and thus are of interest from the standpoint of their relations to behavior.